|Publication number||US8086396 B1|
|Application number||US 11/634,986|
|Publication date||Dec 27, 2011|
|Filing date||Dec 7, 2006|
|Priority date||Dec 7, 2006|
|Also published as||US8160809, US20110224844|
|Publication number||11634986, 634986, US 8086396 B1, US 8086396B1, US-B1-8086396, US8086396 B1, US8086396B1|
|Inventors||Mark Lalon Farwell, Chad Martin Seldomridge, Robert Eric Larson|
|Original Assignee||Itt Manufacturing Enterprises, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (11), Referenced by (8), Classifications (12), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Vehicle leader-follower systems are used in various military and transportation applications in which one vehicle, called the “leader”, moves along the ground, in the air, or space, and one or more other vehicles, each called a “follower”, are to follow the leader and/or move along laterally displaced from the leader.
A leader-follower system approach known in the art is one in which the follower follows closely behind or spaced from the leader, such as less than one second from the leader. In current close leader-follower systems, the follower is too slow to respond to changes in speed and bearing of the leader. The follower must first observe or be communicated the change in speed and bearing of the leader before providing inputs to its controls to adjust its own trajectory in order to stay at the proper offset distance from the leader. Thus, there is an inherent delay between the leader changing its speed and/or bearing and the follower changing its speed and/or bearing. This inherent delay causes poor performance in maintaining the same path as the leader and the proper follow distance unless the follow distance is greater than the leader speed multiplied by the sensing and communications delay time.
In ground vehicles and air vehicles, the time for the vehicle to react to an input change is generally on the order of a one second or more. This reaction time provides for a lower limit on the follow distance using a conventional leader-follower approach. Limiting the follow time interval to two seconds or more is unattractive for many applications because this sets the maximum follow distance to be as much as 80 feet at 30 MPH, for example, and 160 feet at 60 MPH. For certain leader-follower applications, such large follow distances are not acceptable.
Thus, a leader-follower system and method is needed that can allow relatively close following of a leader vehicle without sacrificing vehicle speeds.
Briefly, a method is provided for automatically controlling a first vehicle (follower vehicle) that is to follow a second vehicle (leader vehicle) in a desired manner with respect to movement of the second vehicle. In the follower vehicle, bearing and acceleration control inputs are generated based on data representing bearing and acceleration control inputs made at the leader vehicle and a position of the follower vehicle relative to the leader vehicle so as to mimic in the follower vehicle the bearing and acceleration control inputs made in the leader vehicle.
According to one embodiment, the follower control method comprises three control loops. In a first control loop that has the lowest latency of the three control loops, the bearing and acceleration control inputs in the leader vehicle are monitored. Control status signals are generated representing the bearing and acceleration control inputs in the leader vehicle, and the control status signals are transmitted to the follower vehicle. The follower vehicle receives the control status signals from the leader vehicle and adjusts bearing and acceleration control inputs in the follower vehicle based on the control status signals received from the leader vehicle at a time so that the bearing and acceleration control inputs are made in the follower vehicle at substantially the same location that the corresponding bearing and acceleration control inputs were made on the leader vehicle.
In a second control loop, a deviation in the velocity of the follower vehicle and the velocity of the leader vehicle is monitored. First bias data is generated for adjusting the bearing and acceleration control inputs in the follower vehicle based on the velocity deviation.
In a third control loop, deviation between estimated follow distance and lateral offset of the follower vehicle with respect to the leader vehicle and target follow distance and target lateral offset is monitored. Second bias data for adjusting the bearing and acceleration control inputs in the follower vehicle is produced based on the deviation in follow distance and lateral offset.
The update rates of the second and third control loops may be progressively slower frequencies than the update rate of the first control loop. Furthermore, data produced in the second and/or third control loops may be used to adjust a conversion made between data representing the control inputs in the leader vehicle to data for control inputs to be made in the follower vehicle.
The leader vehicle 100 generates and transmits to the follower vehicle 200 leader control status signals that represent leader acceleration and bearing control inputs applied in the leader vehicle 100. The follower vehicle 200 receives the leader control status signals and executes a follower control algorithm with control mimic of the leader acceleration and bearing control inputs. In doing so, the follower vehicle 200 is able to maintain a consistent and desirable follow distance with respect to the leader vehicle 100. The follower control algorithm is described hereinafter. The leader vehicle 100 and follower vehicle 200 may be manned or unmanned (remotely or computer controlled, e.g., robotic) air, ground or space vehicles.
The specific type of sensor used for the function of the throttle sensor 130 depends on the type of motive system and throttle control used in the leader vehicle. For example, if the throttle control consists of a mechanical lever, pedal or other mechanical element, then the mechanical displacement encoder may comprise a mechanical displacement encoder that measures displacement of a mechanical device and converts the measured displacement to a signal representing an amount of acceleration being applied. Alternatively, the throttle sensor 130 may be a flow gauge that measures flow of a fuel mixture to a motor (representative of the amount of throttle input being applied). Further still, the throttle sensor 130 may be a motor voltage or current probe that measures the amount of current or voltage being applied to an electric motor. Regardless of the specific type of throttle sensor used, the throttle sensor 130 generates a throttle sensor signal representing an amount of acceleration being applied in the leader vehicle 100.
Similarly, the specific type of brake sensor 140 used depends on the type of braking system and braking control used in the leader vehicle 100. For example, the brake sensor 140 may comprise a mechanical displacement encoder that measures displacement of a mechanical device (lever, pedal, etc.) and converts the measured displacement to a signal representing an amount of braking being applied. Alternatively, the brake sensor may comprise a flow gauge that measures an amount of hydraulic fluid being applied in a brake line to a brake in the leader vehicle. The braking sensor 140 generates a brake sensor signal representing an amount of braking being applied in the leader vehicle 100.
Again, the specific type of steering sensor 150 depends on the type of steering system used in the leader vehicle 100. The steering sensor 150 may comprise a sensor that monitors rotation of a steering shaft that measures direction and movement of a steering shaft, a wheel deflection encoder that measures deflection of a wheel or a track deflection encoder that measures deflection of a track of a vehicle such as a tank. The steering sensor 150 generates a steering sensor signal representing changes made to the bearing of the leader vehicle.
There are additional optional sensors in the leader vehicle 100 to sense one or more of speed, bearing and position of the vehicle, independent of the control inputs being applied in the leader vehicle. For example, there may be a speed sensor 170, a bearing sensor 172 and a position sensor 174. Alternatively, a global positioning system (GPS) unit shown at reference numeral 176 is provided in the leader vehicle 100 to indirectly measure the speed, bearing and position of the leader vehicle. The extent of optional sensors provided in the leader vehicle is sufficient to transmit data to the follower vehicle(s) to enable the follower vehicle to compute relative speed, relative bearing and relative position of the follower vehicle with respect to the leader vehicle.
The controller 110 receives the signals from the sensors 130, 140 and 150 (and optionally the 170, 172 and 174 or GPS related parameters from speed, bearing and position derived from the GPS receiver 176) via the sensor interfaces 160. The controller 110 formats the sensor data signals and converts the sensor data signals to leader control status signals that represent leader acceleration and bearing control inputs in the leader vehicle in terms of percent effort for leader throttle, brake and steering control inputs. The controller 110 outputs the leader control status signals to the radio transceiver 120 that transmits the signals to the follower vehicle(s). Percent effort may be in universal units of physics, for example, acceleration and braking in terms of meters per second change per second, and steering in terms of degrees of deviation change per second.
As an alternative to GPS, the leader vehicle 100 may use inertial navigation system (INS) techniques that measure changes in acceleration to determine position of the host vehicle. To this end, the leader vehicle 100 may comprise a block of accelerometers 180 and gyroscopes 182.
The speed sensor 270 may comprise a speedometer that measures absolute speed of the follower vehicle 200. The bearing sensor 272 may comprise an electronic compass that measures absolute bearing of the following vehicle 200. The ranging sensor 274 is provided to view the leader vehicle 100 from the follower vehicle 200 in order to compute relative velocity, relative position and relative bearing of the follower vehicle 200 with respect to the leader vehicle 100. For example, the ranging sensor 274 may comprise a video camera system, a ranging sensor such as a RADAR sensor or laser imaging detection and ranging (LIDAR) sensor. Further still, the follower vehicle 200 may comprise a block of accelerometers 280 and gyroscopes 282 to enable INS computations.
The follower control algorithm described herein employs direct observation to perform tracking of the follower with respect to the leader. This observation may be performed on the follower, or on the leader and the observation information transmitted to the follower. Only relative position of the follower with respect the leader is needed, although relative position and relative bearing (velocity vector) of the follower with respect to the leader may improve performance. Providing a GPS unit in both the leader and the follower, and transmission of GPS information from the leader to the follower is one way to accomplish computation of relative position and relative velocity. An alternative to using GPS is to use the ranging sensor 274 on the follower vehicle. Still another alternative is to use INS techniques on both the leader and follower, and to transmit INS data from the leader to the follower, similar to that for the GPS data.
Turning now to
With reference to
At this point, the updated percent effort is still in terms of the leader vehicle's control inputs. At 430, a percent effort mimic model is used to convert from leader percent effort to follower percent effort for the acceleration and bearing control inputs. The percent effort mimic model is a calibration computation that converts leader percent effort to follower percent effort. The percent effort mimic calibration may be determined a priori from knowledge about the controls and control input sensors on the leader vehicle and the controls on the follower vehicle. In addition, the type of motive system used on the leader vehicle and the follower vehicle may be relevant to the percent effort mimic model. The percent effort mimic model may be represented by a point-slot plot that maps percent effort of the leader to percent effort of the follower. Adjustments may be made to the percent effort mimic model based on data generated in the other control loops as described hereinafter.
Next, at 440, the throttle, brake and steering controls in the follower are made according to the follower percent effort data computed at 430 for the current update cycle using the most recent bias data from the control loops 500 and 600. In one embodiment, the control loop 400 is updated at a frequency of 10-20 Hz.
With reference to
Turning now to
The three control loops 400, 500 and 600 operate concurrently, albeit at different update cycles, ultimately to produce highly accurate updates (at 440) to the controls of the follower vehicle.
It should be understood that the follower control algorithm described herein may be implemented where one or more of the vehicles involved may employ a so-called “drive-by-wire” vehicle control system in which electrical signals are produced in response to control mechanisms (steering wheel, accelerator pedal, throttle lever, brake pedal, etc.) to control the steering/bearing and acceleration of a vehicle. In a leader vehicle that uses “drive-by-wire” control technology, the signals produced for each of the relevant controls would be monitored in the leader vehicle and used to directly determine a measure of percent effort that is transmitted to one or more follower vehicles. If a follower vehicle also uses “drive-by-wire” control technology, then the conversion from leader percent effort to follower percent effort is as described above to produce the electrical follower control input signals.
The system and methods described herein may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative and not meant to be limiting.
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|U.S. Classification||701/482, 340/961, 342/63, 340/967, 342/30, 701/4|
|International Classification||G01S13/00, G08B23/00, G05D1/08, G01C21/00|
|Dec 18, 2006||AS||Assignment|
Owner name: ITT MANUFACTURING ENTERPRISES, INC., DELAWARE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FARWELL, MARK LALON;SELDOMRIDGE, CHAD MARTIN;LARSON, ROBERT ERIC;SIGNING DATES FROM 20061127 TO 20061201;REEL/FRAME:018647/0748
|Jan 27, 2012||AS||Assignment|
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Effective date: 20111221
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|Dec 15, 2016||AS||Assignment|
Owner name: HARRIS INTERNATIONAL, INC., FLORIDA
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